1. Field of the Invention
The present invention relates to a display module, such as a liquid crystal display module, and more particularly to the fitting parts for installing a display module.
2. Background Art
Aside from the fact that they are low on power consumption and are thin and lightweight, liquid crystal display devices have come to be widely used for display equipment because of their portability, such as personal digital assistants (PDAs) and cell phones, and for movable display equipment, such as car navigation systems.
Such liquid crystal display devices normally comprise a liquid crystal display panel, an optical sheet such as a diffusing plate, a prism sheet, a light guide plate, a reflector plate, a plastic frame that encloses the aforementioned items, a lamp set located close to the side edges of the light guide plate, a base plate that houses these items and covers the back of the liquid crystal display device, and a front frame that covers the circumferential front portion of the liquid crystal display panel and the sides of the assembly.
Gate driver ICs and source driver ICs are mounted onto the liquid crystal panel by means of Tape Automated Bonding (TAB) and are driven by a printed circuit board carrying control circuits connected to them.
A liquid crystal display (LC) module used in car navigation systems is hereafter described with reference to FIG. 1, which is an exploded perspective view of the present invention showing the LC module 10 of a car navigation system seen from an angle from below.
The LC module 10 comprises the following component elements which are combined together and housed by a plastic frame 14: an LC panel 11 in which an array substrate and a substrate facing it are adhered together by sealing material and liquid crystal is filled in the space between the two substrates; drive ICs (not shown in the figure) composed of gate driver ICs and source driver ICs for driving the LC panel 11 that are provided directly on the end edges of the array substrate of the LC panel 11 by means of the chip on glass (COG) method; flexible printed circuit (FPC) boards 12a and 12b for connection to a control circuit board (not shown in the drawing) that is connected to the various drive ICs of LC panel 11 and carries controllers and other electronic parts that control such drive ICs; a plurality of optical sheets 15a to 15c disposed on the back surface of the LC panel 11; a rectangular, tabular light guide plate 17 made of acrylate resin; a white reflector plate 18 disposed on the back surface of the light guide plate; and a rear case 19 that covers the back surface of the reflector plate. The top part of the plastic frame 14 supports the LC panel 11, the other structural elements being fitted into the bottom part of the plastic frame 14. To complete the assembly, a front frame 22 is applied to the front of the LC panel 11 so as to fit the rear case 19.
Eaves 23 are located around the light guide plate 17 along its side edges, and a tubular lamp 21 is disposed in a lamp housing 24 that is a gap formed inside the plastic frame 14 by the reflector plate 18 and the eaves 23 of the light guide plate 17. The tubular lamp 21 is disposed in such manner that its light exit surface is parallel to the side edges of the light guide plate 17, which constitute the light entry surfaces of the plate, the plate being made of transparent acrylate resin or like material. The flexible printed circuit boards 12a and 12b wind to the side and the rear of the plastic frame 14, and are connected to a printed circuit board, (not shown in the drawing), that is installed to the back surface of the rear case 19. The printed circuit board is covered by a metallic cover, with an insulating sheet (not shown in the drawing) interposed.
Since liquid crystal display devices are generally used while one is in transit, they must be firmly and compactly made.
In a car navigation system, for instance, the space allotted for their installation is restricted to the space beneath the car's dashboard. In the conventional installation method disclosed in Japanese Patent No. 3532315 (refer to FIG. 8), where specifically, an LC panel 93, a backlight 94a, a heat radiator 94b and a control unit 96 are held in place by being screwed to the mounting frame of a front chassis 91 that encloses them on each side and is itself held in place by the rear chassis 92 of the navigation system provided in the place of installation, a certain amount of depth is required to attach the mounting frame of the front chassis 91 to the rear chassis 92. In other words, an exclusive mounting frame must be configured to have a certain size and depth for fastening the LC module. Designing compact car navigation systems has become an issue considering that their size must conform to the prescribed outer dimensions of their installation location.
In another attaching method illustrated in FIG. 9, four screw holes 119b, into which screws for fastening the chassis frame are screwed, are provided on four corners of the rear case 119, for the purpose of attachment to the vehicle. These portions are formed through a well-known process termed “pressing”, whereby a circular dish-shaped die is stamped into the sheet metal of the rear case 119, the screw holes 119b being made in the center of the circular dish-shaped protruding pressed portions 119a that rise up on the back surface. This mode of construction is widely known since it merely involves embossing the rear case.
Although they are disposed as close to the edge of each corner of the rear case 119 as possible, the screw holes 119b must not, for processing reasons, reside excessively close to the edges, since they are formed as circular dish shapes. In addition, the screw holes 119b could obstruct the fastening of the printed circuit board onto which the drive ICs and control circuits, etc., are mounted, and which is installed behind the rear case 119, and the rear cover (not shown in the drawing) that covers it.
In recent years, LC modules have become multi-functional and very advanced, so that various ICs and parts are mounted onto the printed circuit board so as to realize a variety of functions, with the result that the printed circuit board has become enlarged, while the presence of the circular dish shaped screw holes 119b has imposed restrictions on its size and shape. In other words, it has become problematic to secure space for the printed circuit board.
In FIG. 9, the gate drive ICs and source drive ICs (not shown) are connected via flexible printed circuit boards (represented by reference numerals 112a and 112b in FIG. 9) to a printed circuit board (also not shown).
As can be derived from the above, car navigation systems, etc. require a display module that is entirely compact and has fitting portions that occupy a small space.